The present invention relates to improved valve constructions of the nozzle and impingement plate type.
By way of background, in a nozzle and impingement plate type valve, flow through the valve is controlled by varying the gap between the impingement plate and the tip of the nozzle. In many valves the gap dimension is quite small in relation to the diameter of the nozzle. This is particularly the case for servovalves that are controlled by torque motors which inherently have small angular impingement plate or flapper displacement capability. The fluid metering area in such valves (sometimes referred to as curtain area) is the product of the flow periphery times the nozzle gap. Another significant parameter in such valves is the force required to position the flapper or nozzle in relationship to each other, i.e., to vary the nozzle gap. This force may be expressed as the product of the projected nozzle area (on the flapper) times the pressure drop across the nozzle-impingement plate interface. Thus, for a valve with a given nozzle gap and pressure drop, the flow will increase linearly with nozzle diameter while the operating force increases as the square of the nozzle diameter. It is generally desirable for a valve to have a high ratio of total metering area to projected nozzle area.